1. Field of the Invention
This invention relates to systems and methods for storing electronic data and has applicability to enterprise data backup systems.
2. Description of the Related Art
Improving backup and restore performance is a continuing desire of enterprise data managers. In a typical computing environment, magnetic disk drives are used as the primary storage mechanism for active data, whereas magnetic tapes are used for data backup and archive. The magnetic disks provide rapid and reliable access to data, but they are perceived as being more expensive. In addition, since they are non-removable, they are at risk of physical disasters. Magnetic tape storage is perceived as being less expensive and, because tape cartridges are removable, they can be moved to offsite locations to protect against physical disasters. Therefore, most backup software in use has been optimized for use with magnetic tape technology.
Reading and writing data on a tape requires that the reel be unwound until the desired location is found. Once in the appropriate location, the read or write operation can begin. Because of the mechanical nature of this access, read and write operations are slow and often fail. In many situations, it would be beneficial to provide the random access speed and the reliability of a magnetic disk drive to backup systems while still allowing for the possibility of offsite storage. As a result, a new category of magnetic disk systems is becoming popular called virtual tape technology.
Virtual tape systems are magnetic disk systems that transparently emulate a tape drive and/or a tape library. They provide the same physical connections to a host, such as SCSI, Fibre Channel or Ethernet. This allows them to connect in the same way as the tape systems they are replacing or augmenting. They also provide the same logical response to tape drive and robot commands, which allows the same backup software to remain in use. The emulator is also able to send the host computer the expected tape-drive interrupt signals such as beginning-of-tape, end-of-tape, and inter-record-gap. In this case, such a system can plug right in to an existing tape based storage system without a need for the user to change the storage network or software environment.
Although such systems have been successful in the marketplace, the currently available devices still do not fully take advantage of the properties of disk storage in a way that provides maximum flexibility and usefulness.